Fiber feathering in additive manufacturing

ABSTRACT

An article of manufacture is disclosed that comprises an infill made from linear segments of filament, such as but not limited to continuous carbon fiber-reinforced thermoplastic filament. Feathering approaches are addressed to generate segments of filament in various geometries that distribute where cuts or ends of segments occur or points where two ends of segments are fused or the like to avoid overlap. Aspects of one approach include identifying long edges and eliminating short edges which present acute angles.

This application is related to co-pending U.S. patent application Ser.No. ______ filed on even date herewith, entitled “Generating Tool Pathsto Preserve Filament Continuity in Additive Manufacturing”, AttorneyDocket No. 3019-119US1 which is assigned to the assignee of the presentapplication and incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to aspects of additivemanufacturing of three-dimensional articles, and, more particularly, toimproved techniques for fabricating articles of manufacture employingfiber feathering as addressed further herein.

BACKGROUND

In general, there are two complementary approaches to fabricate anarticle of manufacture: additive manufacturing and subtractivemanufacturing.

Additive manufacturing involves aggregating material to form the desiredarticle of manufacture. In contrast, subtractive manufacturing involvesremoving material to form the desired article of manufacture. Inpractice, many articles of manufacture are fabricated using acombination of additive and subtractive techniques.

A form of additive manufacturing—colloquially known as “3D printing”—isthe subject of intense research and development because it enables thefabrication of articles of manufacture with complex geometries.Furthermore, 3D printing enables the mass customization of articles ofmanufacture with different dimensions and characteristics. See, forexample, U.S. patent application Ser. No. 15/899,361, filed Feb. 19,2018, entitled “Hexagonal Sparse Infill Made of Linear Segments ofFilament,” and U.S. patent application Ser. No. 15/899,360, filed Feb.19, 2018, entitled “Quadrilateral Sparse Infill Made of Linear Segmentsof Filament”, both of which are assigned to the assignee of the presentapplication and incorporated by reference in their entirety. Thereremain, however, many challenges in the design, manufacture, and use of3D printers, as well as, in the advancement of 3D printing processes.

Consider the task of designing an article to be sufficiently strong toresist a wide array of forces encountered in real world usage, butlightweight. An article of a given material, a given external geometry,and a solid interior is typically stronger than an article with a hollowinterior. In contrast, an article of a given material, a given externalgeometry, and a hollow interior is typically lighter than an articlewith a solid interior.

There are, however, more options for the interior and one such option isa sparse infill. A sparse infill (herein also called an “infill”) is aporous or skeletal or cellular structure that is stronger than a hollowinterior and lighter in weight than a solid interior.

Infills are commonly incorporated into articles that are 3D printed, andit is well-known how to make an infill using a 3D printing technology inwhich the structural integrity of the infill is independent of themacroscopic properties of the materials used to make the structure. Forexample, the structural integrity of an infill made of acrylonitrilebutadiene styrene (ABS) is independent of how the plastic is cut up andassembled. It is well-known in the prior art how to make an infill usingABS with fused-deposition modeling (“FDM”).

SUMMARY OF THE INVENTION

In contrast, the structural integrity of the infill is dependent on themacroscopic properties of some materials. For example, the structuralintegrity of an infill made of fiber-reinforced thermoplastic filamentis dependent on how the filament is cut up and assembled. In general,one structural advantage of a fiber-reinforced filament is diminishedwhen the filament is cut, and, therefore, cuts are to be avoided whenpossible and should be strategically placed as addressed further herein.Put otherwise, longer uninterrupted fiber reinforced filament runs aregenerally stronger than shorter runs. Thus, for an article ofmanufacture having an edge or edges requiring extra strength, a longuninterrupted filament run is desirable along such edges.

As noted above, for some materials, such as ABS plastic, thediscontinuity can be addressed by fusing the first and second segmentstogether. But, for other materials, the mere act of cutting the filamentsignificantly weakens the material by cutting internal reinforcingfibers, and fusing the various segments does not fix the problem as analigned series of fused joints is susceptible to failure uponapplication of a shearing force.

Beyond the difficulties addressed advantageously by the relatedapplications addressed above and elsewhere herein, a different class ortype of problem is encountered by article geometries which require afilament to be cut or otherwise applied in a discontinuous manner asshown in FIG. 1A. In FIG. 1A, three filaments 10, 20, and 30 are showneach having an internal reinforcing fiber or fibers represented bydashed lines. While represented by dashes, these fibers are typicallylong continuous fibers. In FIG. 1A, the filaments 10, 20, and 30 havebeen cut or otherwise deposited in a discontinuous manner and then fusedin regions 14, 24, and 34, respectively. As these fused regions 14, 24,and 34 do not include continuous internal reinforcing fibers they areweaker than the remainder of the filaments 10, 20 and 30. As a result, amuch smaller force F₁ is required to damage the aligned fused regions14, 24, and 34 than the force F₂ required to cause damage to thefilaments 10, 20 and 30 where F₂ is applied along a length of filament30 where continuous reinforcing fibers 32 help spread and dissipate thatforce.

In FIG. 1B, regions 14′, 24′ and 34′ in filaments 10′, 20′ and 30′,respectively, have been moved so that that they no longer align. Theseparation of the regions 14′, 24′ and 34′ in the x-dimension ispreferably at least a predetermined distance, d, where that spacing ispossible.

While FIGS. 1A and 1B illustrate an advantageous solution to a problemin the xy plane, the present invention also provides an advantageoustechnique for generating a tool path to distribute starting and endingfilament points across slices in the z-plane as well, as addressedfurther herein in connection with FIG. 21, for example.

Among its several aspects, the present invention recognizes as a generalmatter, when a number of filament strands end in a straight line or endnear each other (see region 320 of FIG. 3, for an example), there is aseam which will be a weaker spot in the part. While a few simple shapesmight have very long uninterrupted filament runs with few cuts, due toprocess or mechanical constraints, there will usually be some spots in atypical part where multiple filaments will have to end near each other.Instead of having them line up in a perfect seam, having them staggeredas shown in FIG. 1B will provide an advantageous benefit. While a longcontinuous filament without a seam or cuts is preferable, this preferredend is difficult to achieve given the process and mechanical constraintsof real world articles of manufacture. Such articles often have bothlong edges and short edges and one or more acute angles between suchedges, as illustrated by an exemplary bicycle frame addressed herein.

As used herein, filament feathering is when the ends of tool pathsdefining runs of material, such as fiber reinforced filament, meet in astaggered pattern as addressed in further detail herein. One presentlypreferred fiber feathering approach addressed herein is an outcome of anedge-offsetting strategy flowing from a tool path generation techniqueto preserve filament continuity used to generate tool paths for materialruns.

Embodiments of the present invention enable an article to be fabricatedwith fiber reinforced filament without some of the costs anddisadvantages for doing so in the prior art. For example, someembodiments of the present invention deposit segments of filament inshapes and locations in which discontinuities would otherwise occur sothat the number of aligned discontinuities, filament cuts, or other weakseams and the like are reduced. Furthermore, some embodiments of thepresent invention deposit segments of filament in shapes and locationsso that the harmful effects of aligned discontinuance are at leastpartially eliminated. In general, this advantageous result is achievedby depositing the segments of filament employing filament feathering tocarefully distribute the locations of filament beginnings and endings,cuts, or discontinuities, and the like.

Embodiments of the present invention are described in detail that enablethe fabrication of a wide variety of articles of manufacture having abetter balance of strength resulting from long uninterrupted lengths offilament where required without an excess of aligned filament cuts ordiscontinuities as addressed further herein.

A more complete understanding of the present invention, as well asfurther features and advantages of the invention, will be apparent fromthe following Detailed Description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B provide a simplified illustration of the type of problempresented by filament discontinuity and an application of filamentfeathering in accordance with the present invention to advantageouslyaddress this problem.

FIG. 2 depicts an illustration of the components of an additivemanufacturing system 100 suitably adapted to provide fiber feathering inaccordance with an illustrative embodiment of the present invention.

FIG. 3 illustrates a top view of a bicycle frame with material runs thatillustrate a weak seam which would result if a print head could beideally controlled to turn with a turning radius of zero.

FIG. 4 illustrates a top view of a single horizontal layer of a portionof a bicycle frame employing filament feathering printed with gaps inaccordance with the present invention.

FIG. 5 illustrates a top view of a single horizontal layer of a portionof a bicycle frame employing filament feathering printed with overlapsin accordance with the present invention.

FIGS. 6A and 6B further illustrate the differences between fiberfeathering with gaps and overlaps, respectively.

FIG. 7 shows a top view of the entirety of the bicycle frame of FIG. 4with four long edges to illustrate an edge-offsetting strategy inaccordance with the present invention.

FIG. 8A shows a first offset edge.

FIG. 8B shows a second offset edge.

FIG. 8C shows a third offset edge.

FIG. 8D shows a fourth offset edge.

FIG. 8E shows a fifth offset edge.

FIGS. 9A and 9B show the starting edges of a bicycle frame and astarting clipping outline of the bicycle frame, respectively.

FIGS. 10A and 10B show offset edge one and clipping outline one side byside.

FIGS. 11A and 11B show offset edge two and clipping outline two side byside.

FIGS. 12A and 12B show offset edge three and clipping outline three sideby side.

FIGS. 13A and 13B show offset edge four and clipping outline four sideby side.

FIGS. 14A and 14B show offset edge five and clipping outline five sideby side.

FIGS. 15A and 15B show offset edge six and clipping outline six side byside.

FIGS. 16A and 16B show offset edge seven and clipping outline seven sideby side.

FIGS. 17A and 17B show offset edge eight and clipping outline eight sideby side.

FIGS. 18A and 18B show offset edge nine and clipping outline nine,respectively, side by side.

FIG. 19 shows a process for filament feathering in accordance with thepresent invention.

FIG. 20 shows a process for edge-offsetting to implement slicing topreserve filament continuity in accordance with the present invention.

FIG. 21 shows a cross-sectional illustration of fiber reinforcedfilaments beginning and ending in a series of horizontal xy plane slicesthat have been further sliced in the z plane to illustrate distributionof the beginnings and endings in the z dimension in accordance withaspects of the present invention.

DETAILED DESCRIPTION

FIG. 2 depicts an illustration of the components of an exemplaryadditive manufacturing system 100 in accordance with the illustrativeembodiments of the present invention. Additive manufacturing system 100comprises: controller 101, build chamber 102, turntable 110, depositionbuild plate 111, robot 121, deposition head 122, filament conditioningunit 129, filament source 130, and thermoplastic filament 131. Thepurpose of manufacturing system 100 is to fabricate articles ofmanufacture, such as illustrative article 151 of FIG. 1, as well as thearticle of FIG. 7, for example. It will be recognized that the teachingsof the present invention are applicable to a wide range of articles ofmanufacture and the particular illustrations herein are exemplary.

Controller 101 comprises the hardware and software necessary to directbuild chamber 102, robot 121, deposition head 122, and turntable 110, inorder to fabricate the article 151 or other desired articles. In lightof the present teachings, it will be clear to those skilled in the arthow to make and use controller 101 to perform filament feathering andtool path generation to preserve filament continuity in additivemanufacturing as addressed further in connection with FIGS. 3-21 below.

Build chamber 102 is a thermally-insulated, temperature-controlledenvironment in which article 151 is fabricated.

Turntable 110 comprises a stepper motor—under the control of controller101—that is capable of rotating build plate 111 (and, consequentlyarticle 151) around the Z-axis (i.e., orthogonal to the build plate). Inparticular, turntable 110 is capable of:

-   -   i. rotating build plate 111 clockwise around the Z-axis from any        angle to any angle, and    -   ii. rotating build plate 111 counter-clockwise around the Z-axis        from any angle to any angle, and    -   iii. rotating build plate 111 at varying rates, and as desired        for a particular application, and    -   iv. maintaining (statically) the position of build plate 111 at        any angle.

Build plate 111 is a platform comprising hardware on which article 151is fabricated. Build plate 111 is configured to receive heated filamentdeposited by deposition head 122.

Robot 121 is capable of depositing a segment of fiber-reinforcedthermoplastic filament from any three-dimensional coordinate in buildchamber 102 to any other three-dimensional coordinate in build chamber102 with deposition head 122 at any approach angle. To this end, robot121 comprises a multi-axis (e.g., six-axis, seven-axis, etc.),mechanical arm that is under the control of controller 101. Software forcontroller 101 generates tool paths to generate feathering as addressedfurther herein. The mechanical arm comprises first arm segment 123,second arm segment 124, and third arm segment 125. The joints betweenadjoining arm segments are under the control of controller 101. Anon-limiting example of robot 121 is the IRB 4600 robot offered by ABB.

The mechanical arm of robot 121 can move deposition head 122 in:

-   -   i. the +X direction,    -   ii. the −X direction,    -   iii. the +Y direction,    -   iv. the −Y direction,    -   v. the +Z direction,    -   vi. the −Z direction, and    -   vii. any combination of i, ii, iii, iv, v, and vi,        while rotating the approach angle of deposition head 122 around        any point or temporal series of points. While the present        application is explained utilizing an x, y, z coordinate system,        it will be appreciated the present teachings can be translated        to other coordinate systems if desired. Further, while the robot        121 can be controlled as addressed above, it can also be more        simply implemented and controlled more simply in an xy plane and        then stepped up a step in the z plane, an operation sometimes        referred to as 2.5D.

Deposition head 122 comprises hardware that is under the control ofcontroller 101 and that deposits fiber-reinforced thermoplastic filament131. Deposition head 122 is described in detail in pending United Statespatent applications:

-   -   (i) Ser. No. 15/827,721, entitled “Filament Guide,” filed on        Nov. 30, 2017;    -   (ii) Ser. No. 15/827,711, entitled “Filament Heating in 3D        Printing Systems,” filed on Nov. 30, 2017;    -   (iii) Ser. No. 15/854,673, entitled “Alleviating Torsional        Forces on Fiber-Reinforced Thermoplastic Filament,” filed on        Dec. 26, 2017;    -   (iv) Ser. No. 15/854,676, entitled “Depositing Arced Portions of        Fiber-Reinforced Thermoplastic Filament,” filed Dec. 26, 2017;        all of which are incorporated by reference in their entirety and        particularly for the purpose of describing additive        manufacturing system 100 in general, and deposition head 122 in        particular. The following patent applications are incorporated        by reference for their description of how to make and use        additive manufacturing system 100:    -   U.S. patent application Ser. No. 15/438,559, filing date Feb.        21, 2017;    -   U.S. patent application Ser. No. 15/375,832, filing date Dec.        12, 2016;    -   U.S. patent application Ser. No. 15/232,767, filing date Aug. 9,        2016;    -   U.S. patent application Ser. No. 14/574,237, filing date Dec.        17, 2014; and    -   U.S. patent application Ser. No. 14/623,471, filing date Feb.        16, 2015.

Filament conditioning unit 129 comprises hardware that pre-heatsfilament 131 prior to deposition.

Filament 131 comprises a tow of reinforcing fibers that is substantiallyparallel to its longitudinal axis. In accordance with the illustrativeembodiments, filament 131 comprises a cylindrical towpreg of contiguous12K carbon fiber that is impregnated with thermoplastic resin.Thermoplastic filament 131 comprises contiguous carbon fiber, but itwill be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention in which thermoplastic filament 131 has a different fibercomposition.

It will be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention in which filament 131 comprises a different number of fibers(e.g., 1K, 3K, 6K, 24K, etc.). It will be clear to those skilled in theart, after reading this disclosure, how to make and use alternativeembodiments of the present invention in which the fibers in filament 131are made of a different material (e.g., fiberglass, aramid, carbonnanotubes, etc.).

In accordance with the illustrative embodiments, the thermoplastic is,in general, a semi-crystalline polymer and, in particular, thepolyaryletherketone (PAEK) known as polyetherketone (PEK). In accordancewith some alternative embodiments of the present invention, thesemi-crystalline material is the polyaryletherketone (PAEK),polyetheretherketone (PEEK), polyetherketoneketone (PEKK),polyetheretherketoneketone (PEEKK), or polyetherketoneetherketoneketone(PEKEKK). As those who are skilled in the art will appreciate afterreading this specification, the disclosed annealing process, as itpertains to a semi-crystalline polymer in general, takes place at atemperature that is above the glass transition temperature, Tg.

In accordance with some alternative embodiments of the presentinvention, the semi-crystalline polymer is not a polyaryletherketone(PAEK) but another semi-crystalline thermoplastic (e.g., polyamide (PA),polybutylene terephthalate (PBT), poly(p-phenylene sulfide) (PPS), etc.)or a mixture of a semi-crystalline polymer and an amorphous polymer.

When the filament comprises a blend of an amorphous polymer with asemi-crystalline polymer, the semi-crystalline polymer can be one of theaforementioned materials and the amorphous polymer can be apolyarylsulfone, such as polysulfone (PSU), polyethersulfone (PESU),polyphenylsulfone (PPSU), polyethersulfone (PES), or polyetherimide(PEI). In some additional embodiments, the amorphous polymer can be, forexample and without limitation, polyphenylene oxides (PPOs),acrylonitrile butadiene styrene (ABS), methyl methacrylate acrylonitrilebutadiene styrene copolymer (ABSi), polystyrene (PS), or polycarbonate(PC). As those who are skilled in the art will appreciate after readingthis specification, the disclosed annealing process, as it pertains to ablend of an amorphous polymer with a semi-crystalline polymer, takesplace generally at a lower temperature than a semi-crystalline polymerwith the same glass transition temperature; in some cases, the annealingprocess can take place at a temperature slightly below the glasstransition temperature.

When the filament comprises a blend of an amorphous polymer with asemi-crystalline polymer, the weight ratio of semi-crystalline materialto amorphous material can be in the range of about 50:50 to about 95:05,inclusive, or about 50:50 to about 90:10, inclusive. Preferably, theweight ratio of semi-crystalline material to amorphous material in theblend is between 60:40 and 80:20, inclusive. The ratio selected for anyparticular application may vary primarily as a function of the materialsused and the properties desired for the printed article.

In some alternative embodiments of the present invention, the filamentcomprises a metal. For example, and without limitation, the filament canbe a wire comprising stainless steel, Inconel® (nickel/chrome),titanium, aluminum, cobalt chrome, copper, bronze, iron, precious metals(e.g., platinum, gold, silver, etc.).

To design an article of manufacture, such as article 151 or a bicycleframe like the one shown in FIG. 7, a human designer uses acomputer-aided-design system (e.g., Dassault Systemes SolidWorks®, etc.)to specify the desired spatial, structural, and other physicalproperties of the article of manufacture. The salient spatial featuresof a single slice of an article in the xy plane are depicted in FIGS.4-18B. The human designer and computer-aided-design system select aninfill archetype for article 151, and generate a fully-custominfill—based on the selected infill archetype—for article 151 thatsatisfies the structural and other physical properties with theadaptations and modifications addressed further below.

In accordance with the first illustrative embodiment, each segment ineach layer has—after deposition—a thickness of 500 μm or 0.5 mm, and,therefore, each layer has a thickness of 0.5 mm. It will be clear tothose skilled in the art, however, after reading this disclosure, how tomake and use alternative embodiments of the present invention in whicheach segment in each layer has—after deposition—another thickness.Furthermore, it will be clear to those skilled in the art, after readingthis disclosure, how to make and use alternative embodiments of thepresent invention in which one or more layers has a different thicknessthan one or more other layers.

FIG. 3 shows a slice in the xy plane of a part, a bicycle frame, 300that is generated by creating concentric offset paths from the outlineedges of the part 300. The paths are shown as continuous through a sharpangle 310, and at some point are not possible to print given currentconstraints which limit the printhead to a turning radius of about 20mm. In FIG. 3, while long continuous material paths are shown, a largenumber of paths terminate into each other at a sharp angle. The fiberends, such as end 325, in region 320 all are in a straight line andwould cause a weak seam in the part even if it was possible to printcontinuously through the sharp angle. Such a seam is weak since thesharp angle turn of the fibers within the filament does not allow much,if any, stress to get dissipated by the fibers. In accordance with theillustrative embodiments, article 300 is 81.3 cm by 45.7 cm by 2.0 cm.These dimensions are for a representative bike frame test part. It willbe clear to those skilled in the art, after reading this disclosure, howto make and use alternative embodiments of the present invention tomanufacture actual bicycle frames having differing widths, lengths, anddepths, such as 73 cm×58 cm×6.4 cm, as well as a wide variety ofdifferent articles as desired.

An alternative xy plane slice of a portion of an article or part 400 isshown in FIG. 4. By contrast, with FIG. 3, FIG. 4 shows an example offiber feathering in accordance with the present invention applied to apart 400 which again may suitably be a bicycle frame. As addressedfurther below, the feathering in region 420 is a result of offsettingfrom some of the edges of the part, but not all the edges seen in theentire outline of the part. It is seen that the edges terminate intoeach other in a staggered fashion with gaps as illustrated in greaterdetail in FIG. 6A. It will be noted that the filament segments shown inFIGS. 6A and 6B have fiber reinforcement which is not illustrated inthese figures.

The section of the part 400 in region 420 is weaker than in some otherregions but is better than having the edges all aligned in a single lineas shown in FIG. 3. It will also be noticed in this image that there isa little bit of a gap between the path ends. In this embodiment, it hasbeen chosen to have a gap instead of an overlap between two fibers. Inthis regard, it will be recognized that the heated filament will tend tospread so that any small gaps will tend to fill. In contrast, whereoverlaps are employed while gaps are eliminated any unevenness canpossibly propagate upwards in the z-direction.

FIG. 5 shows an alternative feathering arrangement with overlaps and nogaps of an alternative part 500. The feathering is seen in regions 520,530 and 540 and the laps are most clearly seen in regions 530 and 540and are further illustrated in FIG. 6B.

There are pros and cons to both gaps and overlaps. Gaps are generallypreferred because an overlap can cause excess material build up and thusresult in issues in printing on top of them. With gaps, usually someexcess material will fill in the voids as filament is deposited, butsmall gaps may still remain and the area filled only with spread withoutreinforcing fiber will still present a weaker area.

FIG. 7 shows a top view of the entirety of an xy slice of bicycle frame700 portions 400 and 500 of which are shown in FIGS. 4 and 5. Consistentwith a design goal of long uninterrupted edges, four long edges 702,704, 706, and 708 are identified. A portion of long edge 702 correspondsto a down tube of the bicycle frame 700. Another portion comprises abottom bracket. A portion of long edge 704 corresponds to a chainstayand a further portion comprises a seat tube. A portion of long edge 706defines a top tube.

Toward the end of avoiding the problems illustrated in FIG. 3, forexample, short edges 712, 714, and 716 are identified and omitted aspart of the design process to eliminate or reduce sharp corners andacute angle turns by the print head. Thus, when a first material run oredge path 702 is printed, it starts near omitted edge 716 and is cut orended just before reaching omitted edge 712. Similarly, second and thirdmaterial runs or edge paths 704 and 706 begin and end near theirrespective omitted edges 712 and 714 and 714 and 716, respectively. Afourth material run or edge path 708 can begin at a point such as pointx₀ 718 and end there as well. As discussed above, subsequent offsetedges around void or opening 720 will be offset as shown in FIG. 1B andFIG. 8A starting and ending at an offset point x₁ 818, for example. Asfurther shown in FIG. 8E, a further offset edge surrounding void oropening 720 might start and end at point x₂ 820.

In FIG. 8A, a first offset edge 801 is generated which is offset fromedge material path or edge 708. As a centerline of edge 708 is spaced adistance the width, w, of edge 708 divided by two from the part'sintended edge, the centerline of offset edge 801 is 3w/2 from theintended edge. In FIG. 8B, a second offset edge 803 is generated besideedge 704. In FIG. 8C, a third offset edge 805 is generated beside edge706. In FIG. 8D, a fourth offset edge 807 is generated beside edge 702.The process continues in FIG. 8E with a fifth offset edge 809 beside thefirst offset edge 801.

As can be seen in FIGS. 8A-8E as each new edge is added, the edge getsclipped or otherwise ended just before it intersects with a previousedge that is already present. Examples of this clipping are when secondoffset edge 803 is added, it is clipped just before it reaches originaledge 702. Similarly, when fourth offset edge 807 is added, it is clippedas it intersects second offset edge 803 in region 840. A result of thisstrategy is fiber feathering in areas 842 and 844 of FIG. 8D,respectively.

To achieve the desired clipping, the present invention advantageouslyemploys a clipping outline that is used to clip the edges to the correctsize as addressed further herein. The present approach maintains adesired two dimensional polygon of the empty space remaining that can befilled with tool paths or material runs. As each edge is added, theclipping outline is updated with the empty space being reducedappropriately. The updated clipping outline is then used to clip thenext edge that is added. As further edges are generated, the clippingoutline is continually updated to maintain an accurate representation ofthe empty space left to be filled. The space remaining once all theedges are generated can be filled with an infill pattern or could beleft empty depending upon design constraints regarding weight, strength,cost and the like.

FIG. 9A shows starting edges 702, 704, 706, and 708 for the bicycleframe 700 corresponding to those shown in FIG. 7 alongside a startingclipping outline 900 having external edge 912 and internal edge 914 asshown in FIG. 9B. Edge 912 surrounds the exterior of the desired bikeframe and edge 914 surrounds void 720. As the edges 702, 704, 706, and708 have a width, w, and are printed with a centerline inset a distancew/2, from where the actual edge of the bicycle frame is desired, thestarting clip outline 900 is established at the actual edge of thebicycle frame as a frame of reference for the external starting edgesand the edge around the void.

In FIG. 10A, first offset edge 1002 is added with its center line 3 w/2from the intended edge of the bicycle frame, the clipping outline 914 isadjustably spaced in from the edge of the void resulting in a newclipping outline 1000 with a portion 1014 surrounding the void moved toa distance 2w from the edge of void 1006 and the other edges moved to adistance w from the intended external edge. The net effect of the firstclipping outline is to rule out filament or material printing outsidethat outline which in turn is advantageously utilized to achieve thedesired clipping and the feathering addressed in connection with FIGS.8B and 8D above.

In FIG. 11A, second offset edge 1102 is added beside existing startingedge 704. In second clipping outline 1100 of FIG. 11B, the clippingoutline portion 1104 along edge 704 is now moved from w to a distance 2wfrom the intended bicycle frame edge.

Similarly, in FIG. 12A, third offset edge 1202 is added in FIG. 12Abeside existing starting edge 706. In third clipping outline 1200 ofFIG. 12B, clipping outline portion 1204 along edge 706 is now moved fromw to a distance 2w from the intended bicycle frame edge.

In FIG. 13A, fourth offset edge 1302 is added beside existing startingedge 702. In fourth clipping outline 1300 of FIG. 13B, portion 1304 ofthe clipping outline along edge 702 is now moved from w to a distance 2wfrom the intended bicycle frame edge.

In FIG. 14A, fifth offset edge 1402 is added beside first offset edge1002 and starting edge 708. In fifth clipping outline 1400 of FIG. 14B,portion of clipping outline 1404 is now moved from 2w to 3w.

In FIG. 15A, sixth offset edge 1502 is added beside second offset edge1102 and starting edge 704. In sixth clipping outline 1500 of FIG. 15B,clipping outline portion 1504 is now moved from 2w to 3w.

In FIG. 16A, seventh offset edge 1602 is added beside third offset edge1202. In the seventh clipping outline 1760 of FIG. 16B, clipping outlineportion 1604 is now moved from 2w to 3w.

In FIG. 17A, eighth offset edge 1702 is added beside offset edge 1302and starting edge 702. In the eighth clipping outline 1700 of FIG. 17B,portion of clipping outline 1704 is now moved from 2w to 3w.

Finally, in FIG. 18A, ninth offset edge 1802 is added beside offsetedges 1802, 1402, 1002 and starting edge 708. Clipping outline 1800 asshown in FIG. 18B is generated. Looking at clipping outline 1800, it isseen that the remaining space is largely concentrated in three voids1810, 1812, and 1814. Depending upon the design parameters of thebicycle frame 700, these voids might be left open or filled using avariety of infill techniques.

In the process and examples above, edge offsetting has been employedwith turns being taken offsetting from each starting edge one by one.All of the tool paths and material runs illustrated are within onelayer. Each edge gets a number of continuous paths offset from it untilthe part is finished.

It will be recognized that another suitable approach is to choose asingle dominant edge and to continue offsetting as many paths aspossible from it until the path gets broken up into smaller ones thatare no longer either long or continuous. At that point, offsetting pathsfrom the other non-dominant edges are started. More particularly, apredetermined length can be established and once that length is reached,then other edges can be offset from.

If after a first minimum length is reached, all the remaining edges havesimilar strength requirements, the alternating format discussed above inconnection with FIGS. 9A-18B can be utilized. If all the remaining edgeshave differing strength requirements, the edge having the next higheststrength demand can be utilized as the edge to offset from until theminimum length is again reached.

One reason it may be desired to employ the alternative approach isbecause more strength is desired along a particular edge which may bereferred to as a dominant edge. The more long and continuous fiberreinforced filaments there are following that edge, the stronger thatsection of the part will be.

Once the ability is provided as taught herein to generate tool pathsfrom a dominant edge, the edge which is the dominant edge may vary layerby layer as desired. Layers may be included in the design of an articleof manufacture where all edges hold the same weight as addressed abovein detail. Rotating between all of these options per layer or per secondlayers provides good overall strength in the part as all the layersstack up. Each layer would have a different contribution to the overallstrength of the part due to the dominant edges that have more fiberpaths.

It is further recognized that these approaches may be implemented in2.5D, as well as, true 3D.

In accordance with one design of a bicycle frame, the number of layers Lin the fully-custom infill for article 151 is based on the desiredthickness of the article (i.e., 50 to 60 mm) and the thickness of eachlayer (i.e., 0.5 mm). In particular, the fully-custom infill for article151, in accordance with the first illustrative embodiment, comprises:

$\begin{matrix}{L = {\frac{50 - {60\mspace{14mu} {mm}}}{{.5}\mspace{14mu} {mm}} = {100 - {120\mspace{14mu} {layers}}}}} & \left( {{Eq}.\mspace{11mu} 1} \right)\end{matrix}$

It will be clear to those skilled in the art, after reading thisdisclosure, how to make and use alternative embodiments of the presentinvention in which the fully-custom infill comprises a different numberof layers L.

The radius r of the turns in all of the segments is equal to or greaterthan 20 mm

$\begin{matrix}{r \geq \frac{\rho}{2}} & \left( {{Eq}.\mspace{11mu} 3} \right)\end{matrix}$

It will be recognized alternative equipment might have a larger turningradius or that future equipment might have a smaller turning radius.Various turning radii can be readily adapted to given the teachings ofthe present invention.

FIG. 19 shows a process of feathering 1900 in accordance with thepresent invention. In step 1902, a first filament layout for an articleof manufacture is determined without consideration of feathering. Instep 1904, an area or areas within the layout where weakness occurs aredetermined as a result of an alignment of filament ends, an alignment ofacutely angled filament edges or the like. At step 1906, a secondfilament layout applying feathering principles to reduce part weaknessflowing from alignment of filament and the like is devised. In step1908, an article of manufacture is printed employing fiber reinforcedfilament and utilizing the second filament layout. Among the toolsdeveloped by the present invention to implement the process 1900,techniques are provided to sort long edges from short edges. Forexample, straight edges of a potential tool path having a length greaterthan a predetermined length may be identified. More generally, edgeshaving less than a maximum rate of curvature over a length greater thanthe predetermined length are identified. Acute angle turns along anexterior edge of a slice are also identified, as well as, therelationship of such identified acute angle turns to subsequent anglesof redirected tool path movement. For example, a short edge may beidentified as occurring over a distance less than a predetermineddistance between a first acute and a subsequent angle less than apredetermined number of degrees. Any sufficiently short edge may beremoved from the process of generating offset edges as addressed furtherabove.

FIG. 20 shows a process of generating tool paths to preserve continuityof fiber reinforced filaments 2000 in accordance with the presentinvention. In step 2002, a clipping outline comprising a two dimensionalpolygon for a part to be printed is established. This clipping outlinemaintains a record of the empty space that can be filled with materialpaths or runs. If the cross-section of the desired three dimensionalpart varies, the clipping outline for each side will be varied toreflect such variation as needed.

In step 2004, a first edge, a material run, is added utilizing theclipping outline to clip the first edge when another edge in theclipping outline is reached. For example, when edge 704 reaches theportion of clipping outline 912 corresponding to omitted edge 712.

In step 2006, the clipping outline is updated to reflect the spaceremaining after the first edge is added in step 2004.

In step 2008, a second edge is added utilizing the updated clippingoutline from step 2006 to clip the second edge.

In step 2010, the clipping outline is updated to reflect the spaceremaining after the second edge is added.

In step 2012, the process is repeated until all needed edges have beenadded.

The presently preferred approach to generating tool paths to preventweak spots as a result of the alignment of material run starts and stopscan advantageously also be applied in the z dimension, as well as the xyplane. For cyclic paths which repeat across slices, it is not desirableto have all the start and end points line up across all or multiplelayers in the part. As was the case in the xy plane, such alignmentwould cause a weak seam in the part where it is more likely to fail. Asseen in FIG. 21, starts s₁, s₂, s₃, s₄ . . . s_(n-1) and ends e₁, e₂,e₃, e₄ . . . e_(n-1) and e_(n) are shown for layers or slices I₁, I₂,I₃, I₄ . . . I_(n-1) and I_(n). FIG. 21 shows a cross-section or slicein the z-dimension to illustrate in broad terms, a distribution ofstarts and stops across layers or slices of the bike frame 700.

To address the issue, an algorithm has been implemented to distributethe starts of cyclic paths. Another constraint utilized is that it ismuch less desirable to start or end a path on a curve. So, in additionto distributing the starts, it is desirable to put them in locationswhere the filament will be relatively straight. Consequently, all of thestraight segments of a path are first identified. After identifyingthese regions, the path is analyzed looking for a starting point that isat least a predetermined distance away from all the other start pointsthat have been determined so far. This distance is advantageously a userestablished parameter. When checking if a point is far enough away fromother points, the algorithm has been designed to only look a certainnumber of layers below the current layer. This number is again a userselectable parameter. Once a suitable start point is established thearray of points defining the tool path is rotated so the path starts atthe point. It is possible that no ideal starting point can be found, inwhich case, a random location can be selected. It will be recognized analternative approach can be employed in which constraints are graduallyloosened until a point meeting the loosened constraints is picked.

For the user selectable parameters, a minimum separation of 5-40 mm and2-5 layers down are possible ranges to be selectable from.

It is to be understood that the above-described embodiments are merelyillustrative of the present invention and that many variations of theabove-described embodiments can be devised by those skilled in the artwithout departing from the scope of the invention. It is thereforeintended that such variations be included within the scope of thefollowing claims and their equivalents.

For example, while the present invention is described in the context ofpresently preferred systems and materials, it will be recognized thatthese systems and materials are likely to evolve with time and that thedisclosed solutions to problems are generally applicable to additivemanufacturing contexts, where these problems arise.

Also, while many of the originally filed claims are directed to articlesof manufacture, it will be understood that machines and processes aredescribed herein and may also be claimed by this application or acontinuation hereof.

What is claimed is:
 1. An article of manufacture having across-sectional slice with at least a first long edge, a second longedge, and one short edge joining the first edge and the second edgecomprising: a first material run beside the first long edge extendingfrom near one end of the first edge to near the first long edge's otherend without crossing said at least one short edge a second material runbeside the second long edge from near a first end to near the secondlong edge's other end, the second material run ending without crossingthe first material run and without crossing said at least one short edgea third material run beside the first material run, the third materialrun extending substantially along the first material run's lengthwithout crossing the first material run, the second material run andsaid at least one short edge; additional material runs to form the crosssectional slice without crossing previous material runs and said atleast one short edge, wherein ends of material runs are not aligned tocause weak spots.
 2. The article of manufacture of claim 1 wherein thematerial runs comprise lengths of fiber reinforced filament.
 3. Thearticle of manufacture of claim 1 further comprising: adding additionalcross-sectional slices to form the article of manufacture.
 4. Thearticle of manufacture of claim 1 wherein the first long edge isidentified as a dominant edge requiring additional strength.
 5. Thearticle of manufacture of claim 1 wherein at least two ends of thefirst, second, and third and additional material runs are feathered in astair step arrangement.
 6. The article of manufacture of claim 1 whereinplural material runs are added along the dominant edge.
 7. The articleof manufacture of claim 1 comprising a bicycle frame.
 8. A method ofprinting a three dimensional article to be fabricated from a series ofadditive material runs, the additive material runs comprising lengths offiber reinforced filament, the method comprising: analyzing across-section of the three dimensional article to assess edges in thecross-section based at least on length of said edges to identify atleast a first long edge and a second long edge and at least one shortedge joining the first and second long edges; printing a first materialrun beside the first long edge extending from near one end of the firstling edge to near the first long edge's other end without crossing saidat least one short edge; printing a second material run beside thesecond long edge from near a first end to near the second long edge'sother end, the second material run ending without crossing the firstmaterial run and without crossing said at least one short edge; printinga third material run beside the first material run, the third materialrun extending substantially along the first material run's lengthwithout crossing the first material run, the second material run andsaid at least one short edge; and printing additional material runs toform the cross sectional slice without crossing previous material runsand said at least one short edge, wherein ends of material runs are notaligned to cause weak spots.
 9. The method of manufacture of claim 8wherein the material runs comprise lengths of fiber reinforced filament.10. The method of claim 8 further comprising: printing additionalcross-sectional slices to form the article of manufacture.
 11. Themethod of claim 8 wherein the first long edge is identified as adominant edge requiring additional strength.
 12. The method of claim 8wherein at least two ends of the first, second, and third and additionalmaterial runs are feathered in a stair step arrangement.
 13. The methodof claim 8 wherein plural material runs are added along the dominantedge.
 14. The method of claim 8 wherein the three dimensional articlecomprises a bicycle frame.
 15. A system of printing a three dimensionalarticle to be fabricated from a series of additive material runs, theadditive material runs comprising lengths of fiber reinforced filament,the system comprising: means for analyzing a cross-section of the threedimensional article to assess edges in the cross-section based at leaston length of said edges to identify at least a first long edge and asecond long edge and at least one short edge joining the first andsecond long edges; a print head printing a first material run beside thefirst long edge extending from near one end of the first long edge tonear the first long edge's other end without crossing said at least oneshort edge; the print head then printing a second material run besidethe second long edge from near a first end to near the second longedge's other end, the second material run ending without crossing thefirst material run and without crossing said at least one short edge;the print head printing a third material run beside the first materialrun, the third material run extending substantially along the firstmaterial run's length without crossing the first material run, thesecond material run and said at least one short edge; and the print headprinting additional material runs to form the cross sectional slicewithout crossing previous material runs and said at least short edge,wherein ends of material runs are not aligned to cause weak spots.
 16. Amethod of printing a three dimensional article to be fabricated from aseries of additive material runs, the additive material runs comprisinglengths of fiber reinforced filament the method comprising: analyzing atool path including cyclically repeated material runs of the threedimensional article to assess starting edges which align across multiplecross-sectional layers. determining if a first straight length of atleast a first predetermined length exists in a first tool path for afirst cross-sectional layer and locating a first start point on thefirst straight length; and determining if a second straight length of atleast the first predetermined length exists in a second tool path for asecond cross-sectional layer immediately on top of the firstcross-sectional layer and locating a second start point on the secondstraight length spaced at least a predetermined distance from the firststart point.
 17. The method of manufacture of claim 16 wherein thematerial runs comprise lengths of fiber reinforced filament.
 18. Themethod of claim 16 further comprising: printing additionalcross-sectional slices to form the article of manufacture.
 19. Themethod of claim 16 wherein the three dimensional article comprises abicycle frame.